R Octantis

R Octantis, also known as HD 40857, is a solitary, red hued variable star located in the southern circumpolar constellation Octans. It has an apparent magnitude that varies in-between 6.4 and 13.2 within 405 days.[3] At is maximum, it is barely visible to the naked eye. The object is located relatively far at a distance of about 1,900 light years based on parallax measurements from Gaia DR3,[2] but is receding with a heliocentric radial velocity of 46 km/s.[6]

R Octantis

The visual band light curve of R Octantis, from AAVSO data[1]
Observation data
Epoch J2000.0      Equinox J2000.0 (ICRS)
Constellation Octans
Right ascension 05h 26m 06.19562s[2]
Declination −86° 23′ 17.7741″[2]
Apparent magnitude (V) 6.4 – 13.2[3]
Characteristics
Spectral type M5.5e[4] (M5.3e – M8.4e[3])
Variable type Mira[5]
Astrometry
Radial velocity (Rv)46±5[6] km/s
Proper motion (μ) RA: 0.540 mas/yr[2]
Dec.: 31.079 mas/yr[2]
Parallax (π)1.7152 ± 0.0862 mas[2]
Distance1,900 ± 100 ly
(580 ± 30 pc)
Details
Mass6.6[7] M☉
Radius466[7] R☉
Luminosity9,304[8] L☉
Temperature2,571[8] K
Other designations
R Octantis, CD−86°52, CPD−86°72, HD 40857, HIP 25412[9]
Database references
SIMBADdata

R Octantis has been known to have a peculiar spectra since 1892.[10] It was revealed to have emission lines in its spectrum in a 1954 paper[11] and was found to be a long period variable a year later.[12] In 1966, R Octantis was officially classified as a Mira variable.[4] Later observations reveal it to have an overabundance of oxygen on its outer layers.[13]

The object has an average stellar classification of M5.5e, indicating that it is a M-type star with emission lines in its spectrum.[4] However, this can range from M5.3 to M8.4e.[3] It is currently on the asymptotic giant branch, generating energy by fusing hydrogen and helium shells around an inert carbon core. As a result, it has expanded to 466 times the radius of the Sun.[7] R Octantis radiates over 9,000 times the luminosity of the Sun from its photosphere at an effective temperature of 2,571 K,[8] which is cooler than most Mira variables.

References
  1. "Download Data". aavso.org. AAVSO. Retrieved 1 October 2021.
  2. Vallenari, A.; et al. (Gaia collaboration) (2023). "Gaia Data Release 3. Summary of the content and survey properties". Astronomy and Astrophysics. 674: A1. arXiv:2208.00211. Bibcode:2023A&A...674A...1G. doi:10.1051/0004-6361/202243940. S2CID 244398875. Gaia DR3 record for this source at VizieR.
  3. Otero, Sebastian (26 April 2011). "R Octantis". AAVSO Website. American Association of Variable Star Observers. Retrieved 21 April 2016.
  4. Keenan, Philip C. (June 1966). "A Catalogue of Spectra of Mira Variables of Types ME and Se". The Astrophysical Journal Supplement Series. 13: 333. Bibcode:1966ApJS...13..333K. doi:10.1086/190139. eISSN 1538-4365. ISSN 0067-0049.
  5. Samus’, N. N.; Kazarovets, E. V.; Durlevich, O. V.; Kireeva, N. N.; Pastukhova, E. N. (January 2017). "General catalogue of variable stars: Version GCVS 5.1". Astronomy Reports. 61 (1): 80–88. Bibcode:2017ARep...61...80S. doi:10.1134/S1063772917010085. eISSN 1562-6881. ISSN 1063-7729. S2CID 125853869.
  6. Gontcharov, G. A. (November 2006). "Pulkovo Compilation of Radial Velocities for 35 495 Hipparcos stars in a common system". Astronomy Letters. 32 (11): 759–771. arXiv:1606.08053. Bibcode:2006AstL...32..759G. doi:10.1134/S1063773706110065. eISSN 1562-6873. ISSN 1063-7737. S2CID 119231169.
  7. Kervella, Pierre; Arenou, Frédéric; Thévenin, Frédéric (2022). "Stellar and substellar companions from Gaia EDR3". Astronomy & Astrophysics. 657: A7. arXiv:2109.10912. Bibcode:2022A&A...657A...7K. doi:10.1051/0004-6361/202142146. eISSN 1432-0746. ISSN 0004-6361.
  8. McDonald, I.; Zijlstra, A. A.; Boyer, M. L. (2012). "Fundamental Parameters and Infrared Excesses of Hipparcos Stars". Monthly Notices of the Royal Astronomical Society. 427 (1): 343–57. arXiv:1208.2037. Bibcode:2012MNRAS.427..343M. doi:10.1111/j.1365-2966.2012.21873.x. S2CID 118665352.
  9. "V* R Oct". SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved 21 April 2016.
  10. Fleming, M. (November 1892). "Stars having peculiar spectra". Astronomy and Astro-Physics. 11: 765–767. Bibcode:1892AstAp..11..765F.
  11. Bidelman, William P. (November 1954). "Catalogue and Bibliography of Emission-Line Stars of Types Later than B." The Astrophysical Journal Supplement Series. 1: 175. Bibcode:1954ApJS....1..175B. doi:10.1086/190007. eISSN 1538-4365. ISSN 0067-0049.
  12. Campbell, Leon (1955). Studies of Long Period Variables. American Association of Variable Star Observers. Bibcode:1955slpv.book.....C.
  13. Jura, M.; Yamamoto, A.; Kleinmann, S. G. (August 1993). "Long-period oxygen-rich optical Miras in the solar neighborhood". The Astrophysical Journal. 413: 298. Bibcode:1993ApJ...413..298J. doi:10.1086/172997. eISSN 1538-4357. ISSN 0004-637X.
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